The present invention relates to a scaffold structure, and more particularly to a scaffold structure that is light in weight, strong and which has a high degree of torsional stability.
Various types of scaffold structure are known. The present applicant has himself previously patented different scaffold structures which are disclosed in U.S. Pat. Nos. 3,760,902 and 3,910,378, respectively. Both of these scaffold structures include a ladder which is supported in use in a vertical orientation by legs at the bottom of the ladder and by outwardly extending support members or arms at the top of the ladder. The support members at the top of the ladder rest against a wall or building or other structure, in use, to keep the ladder vertical. The known scaffold structures further include a platform assembly which is positionable along the ladder at different heights. A user of the scaffold structure stands on the platform assembly when the ladder is vertical and adjacent a structure on which work is to be preformed. As the work progresses the user of the scaffold structure can change the position of the platform assembly in order to change his position relative to the structure being worked on.
The use of a ladder-like structure in these scaffolds influences the degree of torsional stability which they exhibit. The ladder can be thought of as a planar structure in that its thickness dimension is small in comparison to its length dimension and width dimension. Accordingly, even if the ladder is very strong and can support large compressive loads relatively smaller loads will cause it to twist about its longitudinal axis. Therefore, in order to improve its torsional stability the ladder must be made quite strong and this requires massive components with attendant increases in expense and weight.
Additionally, the ladder itself is a relatively expensive component of the prior scaffold structures. The ladder is comprised of a pair of parallel rails having a plurality of rungs extending therebetween. The fabrication of the ladder includes steps of forming a plurality of holes in the rails for receiving the rungs, fitting the rungs into the rail holes, and securing the rungs and rails together. These steps add to the total cost of the prior scaffold structures which incorporate a ladder.
Finally, because the ladder used in the prior scaffold structures is comprised of a plurality of separate parts (rungs and side rails) which must be secured together, there is a continuing problem concerning the reliability of the ladder. Continuous and repeated use of the ladder puts stresses on the joints between the rungs and side rails of the ladder. These joints have a tendency to weaken and loosen so that the ladder itself may have a tendency to actually come apart. This is a substantial safety problem, and it is aggravated with age and use of the scaffold structures incorporating a ladder. It requires that the joints between the rungs and side rails of the ladder be extremely strong and consequently the ladder will be expensive.